The "is a" relationship, as I assume you know, is inheritance, when one class extends another. Say you have a class "Plane" and another class "CommercialAirliner". A commercial airliner "is a" plane, therefore it would extend class Plane. The "has a" relationship is what is called "aggregation". If you design a class called "Engine", and then design a class called "Car". A car "has a" engine. Therefore it would not extend engine, because a car is not an engine. It would therefore include an object of type Engine as one of its instance members. Hope that's clear. ------------------ Michael J Bruesch Codito, ergo sum... I code, therefore I am. My Java Games, I'm quite proud
Michael J Bruesch<br /><i>I code, therefore I am.</i>
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